Synthesis and Characterization of Vanadium Substituted Potassium Tungsten Bronzes, K_xV_yW_1-yO₃

Abstract

A series of vanadium substituted potassium hexagonal tungsten bronzes K x V y W 1-y O 3 (K-HTB) were prepared by conventional solid state method at 800 °C with compositions of x = 0.30 and 0.00 ≤ y ≤ 0.15. A mixture of K-HTB and non bronze phases with y ≥ 0.20 was observed. The proportion of this non bronze phase increases with increasing vanadium content. The non bronze phases in the mixture could not be indexed yet. In contrast, a very small amount of vanadium can be substituted in potassium tetragonal tungsten bronzes (K-TTB) at 800 °C with x = 0.50 and 0.00 ≤ y ≤ 0.02, however at 700 °C vanadium substituted K-TTB can be prepared with 0.00 ≤ y ≤ 0.05. Further substitution of vanadium in K-TTB decomposes to K-HTB and non-bronze phases.

Self-Organized Transformation from Hexagonal to Orthorhombic Bronze of Cs–Nb–W–O Mixed Oxides Prepared Hydrothermally

“…In addition, low Nb concentration promotes the formation of the HTB crystal phase. 24,25 HTB-type phases containing big alkali ions such as Cs + or K + in the hexagonal tunnels lose the catalytic activity observed in the M2-phase but increase the thermal stability of the crystal phase and give rise to interesting optical properties as in the case of the mixed valence compounds K x WO 3 26 or Cs 0.32 WO 3 that behaves as promising photocatalysts. 27 Nb-or V-doped hexagonal tungsten bronze can be obtained by a partial substitution of tungsten by vanadium or niobium, 28,29 although other crystalline structures can be observed depending on the V or Nb contents.…”

“…Cs + ions must play a decisive role in the stability of Cs 0.5 (Nb,W) 5 O 14 , which has low flexibility in composition and needs a precise Nb/W ratio to be formed. − Thus, depending on the Cs and Nb content, the formation of Nb 2 W 3 O 14 , Cs 0.25 [Nb 2.25 W 2.75 O 14 ] (isostructural with the oxidic bronze Mo 5 O 14 ), or orthorhombic Cs 0.5 [Nb 2.5 W 2.5 O 14 ] can be observed. In addition, low Nb concentration promotes the formation of the HTB crystal phase. , HTB-type phases containing big alkali ions such as Cs + or K + in the hexagonal tunnels lose the catalytic activity observed in the M2-phase but increase the thermal stability of the crystal phase and give rise to interesting optical properties as in the case of the mixed valence compounds K x WO 3 or Cs 0.32 WO 3 that behaves as promising photocatalysts . Nb- or V-doped hexagonal tungsten bronze can be obtained by a partial substitution of tungsten by vanadium or niobium, , although other crystalline structures can be observed depending on the V or Nb contents. ,− …”

UV and Visible Light-Driven Production of Hydroxyl Radicals by Reduced Forms of N, F, and P Codoped Titanium Dioxide

“…Nonmetal doping or codoping into the TiO 2 modifies the valence band level of TiO 2 , reducing the effective band gap energy, as shown in Figure 1, and modulating the light absorption into the visible light region [25,26,27,28,29,30]. Although the incorporation of dopant elements can result in the advantage of narrowing band gap energies, dopants can influence charge carrier recombination processes, and the limited solubility of dopants into the bulk materials as well as thermal instability have limited photocatalytic applications of doped TiO 2 materials [31,32,33,34,35].…”